Abstract
Solvents made from a reactive ionic liquid, with an imidazolium cation and pyrrolide anion, and ethylene glycol at a wide compositional range were studied for separations of CO2 at low partial pressures (â0.1 bar up to 1 bar). Thermal analysis and measurements of viscosity and density show compacting of the liquid upon mixing with enhanced stability achieved by hydrogen bonding. A detailed mechanistic study was performed by IR, quantitative NMR, and ab initio calculations that show significant CO2 absorption capacity below 5000 ppm of CO2 in N2. Three reversible routes are found that yield carbonate (major product), carboxylate (moderate), and carbamate (minor) species. With CO2 at 100% RH, bicarbonate along with carbonate species form. The CO2-ethlyene glycol reaction complex, the carbonate anion, is stabilized by the hydrogen bonding and Coulombic interactions, thus preventing evaporation of the solvent during regeneration. This study demonstrates a promising approach to designer green solvents for CO2 separations in open systems such as direct air capture.
| Original language | English |
|---|---|
| Pages (from-to) | 1090-1098 |
| Number of pages | 9 |
| Journal | ACS Sustainable Chemistry and Engineering |
| Volume | 9 |
| Issue number | 3 |
| DOIs | |
| State | Published - Jan 25 2021 |
| Externally published | Yes |
Funding
The authors thank Dr. Nalinda P. Wickramasinghe at the Instrumentation Facility of the Department of Chemistry at CWRU for feedback on the inverse recovery measurements by NMR and Prof. Shane Parker for discussions on transition state calculations. The authors acknowledge the Northeast Ohio High Field NMR Facility and the Soft Material Characterization Laboratories for the access to TGA. The ionic liquid synthesis and CO measurements were supported by an Early Career Faculty grant from NASA’s Space Technology Research Grants Program under Award No. 80NSSC18K1505. The analysis of the absorption mechanism was in part supported by the American Chemical Society Petroleum Research Fund 59520-DNI4. The phase behavior and the physical property characterization of the solvents were supported by the Breakthrough Electrolytes for Energy Storage (BEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0019409. 2
Keywords
- carbon capture
- Carbon dioxide
- Direct Air Capture, DAC
- Gas separations
- Ionic liquid
- Negative emissions science
